There are quite a few threads on this and it can get confusing, so if you get an error on the BitRock Windows version when you try to upload the upgrade file (can't locate it) all you need to do is this:

Open PHP.ini

Find the line starting open_basedir and comment out that line (// open_basedir)

Reboot your machine - I found restarting the servicers was not enough, it needed a full reboot to work.

As I said I know this is elsewhere but I hope this will make it easier for people to find and fix!